1. Field
Certain aspects of the present disclosure generally relate to wireless communications and, more particularly, to a two-step joint demapping algorithm for log-likelihood ratio (LLR) computation of multiple-input multiple-output (MIMO) signal based on sphere decoding.
2. Background
In a transmitter of all modern wireless communication links, an output sequence of bits from an error correcting code can be mapped onto a sequence of complex modulation symbols. These symbols can be then used to create a waveform suitable for transmission across a wireless channel. In general, the symbols can be mapped to various transmit locations in frequency, time, and space. One of the receiver tasks can be to make inferences about the encoder output sequence based on the received symbols, which are generally corrupted by noise and scaled by a (known) complex channel. When the transmit symbols couple in the transmission, as generally occurs when multiple transmit antennas are used to transmit independent spatial streams over identical time/frequency locations, this demapping operation is generally required to account for all of the interfering streams when making (soft) decisions about a stream of interest. This represents the general framework for joint demapping, which is specialized in the present disclosure to a few particular low complexity realizations.